That’s the case with the Zippo hand warmer, although there’s a bit of chemistry involved with its catalytic element that oxidizes the petroleum-based fuel to produce heat in a controlled manner. Another chemical process, exothermic oxidation, is involved in disposable hand packets. Both create heat. One is reusable.

The Zippo hand warmer is pretty simple to use, and over the course of eight to 10 hours it produces a comfortable, steady warmth while stowed in your pocket.

To start producing heat you remove the top half of the polished stainless steel case and remove the platinum burner. Using the enclosed filler-measuring cup, fill the lower half of the case with two cups of Zippo lighter fluid. (Only the first time the unit is used does it need two cupfuls, the directions say. The measuring cup has a handy spout to help prevent spills.

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Next replace the burner and hold a lighter or match to the burner for 10-15 seconds. Replace the cover and place the unit in its cloth bag. It may take a few minutes to become fully operational.

While working there is a slight odor that smells like naphtha.

If for some reason it becomes necessary to stop the heating action, the burner element can be pried off with a knife or pliers (it’s hot, be careful). Place on a nonflammable surface and it will cool after 30 seconds or so.

When cool the burner may be placed carefully back on the base and stored with the knowledge that there likely is fuel remaining in the base.